How to reduce tortoise electrocution mortalities

April 22, 2017 9:12 am

Thousands of tortoises are inadvertently killed by electric fences in South Africa each year. Yet there are simple, practical steps that farmers can take to stop this. Dr Luke Arnot of the University of Pretoria’s Faculty of Veterinary Science, and Steven Molteno of the global network, Local Governments for Sustainability, explain the extent of the problem, and provide solutions.

Angulate tortoise carcasses under the tripwire of an electric fence. Photo: courtesy OF Lynette Rudman

Tortoises have inhabited the earth almost unchanged for over 200 million years, so they are true miniature dinosaurs.

Of the 43 tortoise species that occur across the world, 14 (33%) are found in South Africa. Eleven of these (79%) are endemic to Southern Africa, occuring nowhere else in the world.

In addition, South Africa has one of the rarest tortoise species, the geometric tent tortoise (Psammobates tentorius), and boasts the smallest tortoise species on the planet, the speckled padloper (Homopus signatus). South Africa can therefore be regarded the tortoise ‘capital’ of the world.

Custodians of the species
South Africans, especially farmers, are the custodians of tortoises in our country, and have an obligation to help preserve the species found here.

Most tortoise species in South Africa are small in stature, but some grow considerably larger. Leopard tortoises (Stigmochelys pardalis) are the largest species in South Africa and reach a shell height of 30cm and a weight of over 30kg.

The vast majority of the country’s tortoises are found on private commercial farms and game farms.

Fences have always played a crucial role in farm management to control the movement of livestock and wildlife, and keep unwanted predators and people out of an area. In the past, most fences consisted of various forms of barbed or wire netting.

However, in recent decades, electric fencing has increased in popularity amongst landowners.

Improved technology with regard to electric fencing and solar energy in recent years has made electric fencing an attractive and economical option for some farmers.

Large tracts of land are now fenced in this way, using various designs according to the intended purpose.

Tripwires: a deadly deterrent
Many electric fences are fitted with a low live ‘tripwire’ placed on one or both sides of the fence, 3cm to 15cm above the ground, depending on the topography.

This can assist in preventing game and wildlife from burrowing under the fence and escaping from a protected area.

It can also be placed on the outside of the fence to prevent predators such as caracals or jackals from digging under the fence and gaining access to livestock.

The tripwire carries an alternating current. Placed at a predator’s nose height, it delivers a shock, which generally makes the animal jump away. Certain species react differently to
shocks, however, and this is where the problem comes in.

It is well documented that pangolins (Manis temminckii) curl up when experiencing fear or pain. So, on receiving an electric shock, they often curl up around the live wire and are shocked repeatedly until they die.

Pangolins have now been categorised as endangered.

Other species commonly killed by contact with electrified fences include porcupines, African rock pythons, rock monitors, aardvarks, chameleons, African bullfrogs, leopard toads and other small animals. However, the vast majority of the unintentional victims are tortoises.

An important reason for the high incidence of death among tortoises is that, like pangolins, they also have an instinctive defensive reaction – withdrawing into their shells when they are hurt or frightened.

Therefore, when a tortoise receives a painful electric shock, instead of pulling away from the cause, it withdraws its head and limbs into its shell. In so doing, the shell remains in contact with the live wire. This results in the animal receiving continued shocks.

In addition, like many animals, tortoises often urinate when in pain. This dampens the ground, which assists in conducting the current through the animal.

Receiving this continuous electric shock ultimately results in death from organ failure, direct damage to tissue due to heat or electrolysis, or sun exposure once the animal has been disabled.

In 2008, Andrew Beck based his MSc thesis on the effects of electric fences on various non-target species. He estimated that electric fences were responsible for about 21 000 deaths of non-target species every year in South Africa alone.

In recent online discussions, concerned farmers reported that tortoise populations in large areas of the Karoo had been all but obliterated after low tripwires were installed.

The Solution – simple yet effective
Research, however, has concluded that there are solutions to the problem. Farmers and electric fence contractors can take steps during fence construction to minimise electric fence mortalities among non-target species such as tortoises and pangolins, while still ensuring that the fence fulfils its intended function.

1. Height of tripwire
Raise the tripwire (or lowest live strand of the main fence) as high as possible, ideally to at least 250mm. This means that most tortoises will not even brush against it. Only the largest specimens will come in contact with a 250mm-high tripwire.

2. Distance of tripwire from fence
If possible, set the tripwire 400mm to 500mm away from the main fence. This technique will only help if combined with point 1.

3. Rocky barrier
Place a physical barrier, such as large rocks along the base of the fence, in place. This rocky ‘apron’ should be high enough to divert tortoises and pangolins away from the fence, and prevent them from coming into contact with live electric wires.

It will also go a long way towards preventing predators and other species from pushing or digging under the fence. In fact, it may even obviate the need for a tripwire!

This is an inexpensive option, especially if your farm has rocky terrain.

4. Switch off during the day
If the purpose of the fence is to deter predators and keep them away from sheep, goats
or wildlife, remember that predators such as jackals are typically nocturnal. Tortoises, by contrast, are strictly diurnal.

This means that you can install duty cycle or timer switches on the fence, which turn off the electric current during daylight hours when tortoises are active, and turn it on again at night when predators hunt.

Using such a timer can also help reduce electricity costs by up to 50%.

5. Use mesh lower down
Another option is to use a mesh wire barrier, such as diamond mesh, on the lower section of the fence, instead of installing electrified wires close to the ground. These mesh fences inhibit the movement of small predators and prevent them from getting under the fence, especially if combined with a rock-packed apron. Live wires can still be used higher up on the fence.

These mesh fences inhibit the movement of small predators and prevent them from getting under the fence, especially if combined with a rock-packed apron. Live wires can still be used higher up on the fence.

Tripwires are a major threat to animals such as tortoises and pangolins, and this problem
is not restricted to South Africa. To date, the survival and flourishing of the country’s game species can, to a great extent, be attributed to the interest and sound practices of farmers. We therefore encourage farmers to also spare a thought for smaller wildlife in their decision-making and livestock management.

We therefore encourage farmers to also spare a thought for smaller wildlife in their decision-making and livestock management.